Modern emissions regulations have led to many internal combustion engine applications utilizing SCR systems to reduce NOx down to regulatory levels. SCR catalyst formulations have a preferred temperature operating range where NOx conversion is at highest efficiency. In addition to high efficiency being desirable, higher efficiencies may be required to meet emissions targets depending upon the system design. At very high temperatures, parasitic oxidation reactions of the reductant reagent reduce the total conversion achievable by the SCR system, and increase the operating cost of the system through ineffective losses of the reducing agent. In the period following a cold start operation, it can take a substantial amount of time for the SCR catalyst to reach an effective operating temperature. During operating periods where another aftertreatment component is regenerating, for example a particulate filter, the engine out temperatures can reach very high temperatures that are well into the reductant oxidation temperature regime.